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Stone surface topography of Prague historic monuments over the centuries
Kovářová, K.; Cihla, Michal; Malát, R.; Semerád, M.; Tryml, M.
2022 - anglický
Stonemasons tool traces on stone surface are undoubtably a significant part of monument historic value. As any other profession, stonemasons craft develops over time and has its own specifics in every period. Each work has its own unique pattern and bears traces of individual stonemason workshops, tradition, etc. The study of building stone cutting is based on evolving methods of mechanoscopy and analytical traceology. Stone traceology deals with traces in material and the subsequent reconstruction of tools and the processes of stoneworking. The interpretation of data in terms of determining the actual trace is called a mechanoscopy. When studying a stone surface, the latest 3D modelling technology is used with subsequent analyses by means of Global Mapper software. The use of these methods enables reconstruction of the craftsman’s tools. The presented article is an extract of a study that systematically maps the stone cutting work in the territory of Prague from the oldest buildings to the present day. For example, stonework in 9th century Prague was gradually evolving from simple stone block modelling to sophisticated cutting of blocks in the 12th century. This information can be very useful in the process of monument care.
Klíčová slova:
stone topography; Prague; craftmanship; stonemason tool; tool traces
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Stone surface topography of Prague historic monuments over the centuries
Stonemasons tool traces on stone surface are undoubtably a significant part of monument historic value. As any other profession, stonemasons craft develops over time and has its own specifics in every ...
Creep of oak dowel: various loading and environmental conditions
Hasníková, Hana; Kunecký, Jiří; Hataj, M.
2022 - anglický
For research of timber joints, the crucial role in force distribution inside the joint is played by distribution and variability of stiffness of the dowels. Not only the instant stiffness, but the one that we can encounter after some longer period. Also, this value and its statistical distribution is influenced by many other factors, however, humidity and temperature are in timber (oak) dowels of utmost importance. In the work results of a creep experiment made using a special testing rig is presented. It has been found, that biggest changes in creep behavior are in case if very humid conditions are present, and, also, that cycling the temperature in high humidity conditions can produce about 104% of the original instantaneous displacement. The result is not surprising, however, new insights are made thanks to relatively high number of samples and ability to produce some statistics. Another outcome is relation of dowel stiffness in time to the level of applied stress, which is quantified in the article.
Klíčová slova:
oak dowel; creep; humidity
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Creep of oak dowel: various loading and environmental conditions
For research of timber joints, the crucial role in force distribution inside the joint is played by distribution and variability of stiffness of the dowels. Not only the instant stiffness, but the one ...
Comparison of mechanical properties of wood determined by local gently destructive tests and fully destructive tests on building elements
Drdácký, Miloš; Kloiber, Michal; Valluzzi, M. R.; Casarin, F.
2022 - anglický
Demolition or repair of historic buildings is a valuable source of test materials for testing nondestructive and gently destructive methods for estimating the mechanical properties of built-in wood. The article uses the results of one such opportunity, when it was possible to study the mechanical properties of wood obtained by local measurements on a larger sample of historic and new wooden beams and compare them with the properties calculated from destructive tests of structural elements. Thirty-one wood elements (nineteen recovered from disassembled buildings and twelve new) were subjected to considerately destructive local tests using a loading mini-jack method. In this method, a small loading jack is inserted into a precisely drilled hole and a load test of the wood in compression along the fibers is performed on a part of the hole wall while measuring the achieved deformation under load. Red and white firs, and pine species constituted the recovered elements - red fir and larch the new ones. Destructive tests (in bending and compression) were also carried out on ten recovered and six new elements, and results were correlated with those of considerately destructive tests. Comparison of the assessed mechanical properties shows reasonably good correlation and promising conclusions for practical applications.
Klíčová slova:
considerately destructive tests; mini-jack method; destructive tests; assessment of mechanical characteristics of wood; historic timber
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Comparison of mechanical properties of wood determined by local gently destructive tests and fully destructive tests on building elements
Demolition or repair of historic buildings is a valuable source of test materials for testing nondestructive and gently destructive methods for estimating the mechanical properties of built-in wood. ...
Solving the moving mass problem on large finite element models with modal analysis – estimation of the discrete movement error
Bayer, Jan
2021 - anglický
Solving transient dynamic problems on large finite element (FE) models using a direct integration requires a high sampling rate and therefore also considerable computing times because of the large system matrices. Movement of a mass on a FE model has to follow the discrete pattern of the FEs, and is therefore of a discrete character. This introduces an unknown\nerror into the analytical results. Applying modal analysis (MA) reduces the number of equations used in the subsequent numerical integration by orders of magnitude. Resampling of the mode shapes to the required sampling rate makes it possible to solve the moving mass problem much more quickly and quasi-continuously. The performed comparative analytical study using ANSYS and MATLAB showed that using a discrete movement on the FE mesh when solving a moving mass problem can cause a considerable error.
Klíčová slova:
moving mass; FE analysis; modal analysis; discret-movement error; ANSYS & MATLAB
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Solving the moving mass problem on large finite element models with modal analysis – estimation of the discrete movement error
Solving transient dynamic problems on large finite element (FE) models using a direct integration requires a high sampling rate and therefore also considerable computing times because of the large ...
Description of the quasi-periodic response caused by combined harmonic and random excitation
Náprstek, Jiří; Fischer, Cyril
2021 - anglický
The generalized van der Pol equation exposed to combined harmonic and random excitation can exhibit a quasi-periodic response. The existence of this particular type of response depends on the detuning between the driving and resonance frequencies. The response is stationary for a ”small” or ”large” value of detuning. The contribution specifies in detail the detuning interval in which the quasi-periodic response occurs.
Klíčová slova:
van der Pol equation; resonance; vibrations
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Description of the quasi-periodic response caused by combined harmonic and random excitation
The generalized van der Pol equation exposed to combined harmonic and random excitation can exhibit a quasi-periodic response. The existence of this particular type of response depends on the detuning ...
Numerical study of the air flow around the U-profile
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2021 - anglický
Our contribution deals with the numerical simulations of the air flow around u-profiles at various angles of attack with the aim to investigate their proneness to galloping. The Unsteady Reynolds Averaged Navier- Stokes (RANS) simulations were performed in the COMSOL Multiphysics software, k-ω SST turbulence model was used. The values of the aerodynamic coefficients and Strouhal number were evaluated and the results were compared with the results obtained experimentally in the wind tunnel.
Klíčová slova:
bluff-body aerodynamics; URANS simulation; transversal galloping
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Numerical study of the air flow around the U-profile
Our contribution deals with the numerical simulations of the air flow around u-profiles at various angles of attack with the aim to investigate their proneness to galloping. The Unsteady Reynolds ...
Numerical solution of a stochastic model of a ball-type vibration absorber
Fischer, Cyril; Náprstek, Jiří
2021 - anglický
The mathematical model of a ball-type vibration absorber represents a non-linear differential system which includes non-holonomic constraints. When a random ambient excitation is taken into account, the system has to be treated as a stochastic deferential equation. Depending on the level of simplifcation, an analytical solution is not practicable and numerical solution procedures have to be applied. The contribution presents a simple stochastic analysis of a particular resonance effect which can negatively influence efficiency of the absorber.
Klíčová slova:
stochastic model; Monte Carlo method; stochastic Euler method; dynamical systems; non-holonomic system
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Numerical solution of a stochastic model of a ball-type vibration absorber
The mathematical model of a ball-type vibration absorber represents a non-linear differential system which includes non-holonomic constraints. When a random ambient excitation is taken into account, ...
Aerodynamic wind tunnel testing of U-beams
Hračov, Stanislav; Macháček, Michael
2021 - anglický
The paper presents the outcomes from the experimental testing of the set of slender U-beams in the climatic wind tunnel. All analysed beams have identical basic geometry with the U-shaped cross section given by the side ratio equal to 2 (having the short side perpendicular to the flow), but they differ in the porosity of their flanges and in the depth of their profile. Two depths of the U-profile combined with six different levels of flange porosity are analysed. The U-beams were tested in the smooth flow in order to determine their aerodynamic coefficients for various angles of wind attack. The influences of the depth and porosity onto these coefficients are studied in detail. Moreover, the susceptibility of each individual case to transversal galloping is assessed based on the classical quasi-steady theory. The comparison with the results from the aerodynamic tests of the prisms with rectangular cross-sections having side rations equal to two, four and six is also given and discussed.
Klíčová slova:
wind tunnel testing; aerodynamic coefficients; galloping
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Aerodynamic wind tunnel testing of U-beams
The paper presents the outcomes from the experimental testing of the set of slender U-beams in the climatic wind tunnel. All analysed beams have identical basic geometry with the U-shaped cross ...
Stability of a bar influenced by small and large imperfections
Náprstek, Jiří; Fischer, Cyril
2020 - anglický
The geometrical and physical imperfections of systems can drastically reduce their critical loading. These imperfections are usually of stochastic character and, therefore, they act as random parametric perturbations of coefficients of corresponding differential equations. In this paper, the imperfections are introduced as multidimensional statistics on the set of a large number of realizations of the same system. As far as the amount of information is small or the imperfections themselves cannot be considered small, the convex analysis is preferable. The paper compares results obtained by both stochastic and convex analyses for hyperprism and demonstrates when each of them is more convenient to be used. Besides of the hyper-prism, the possibilities and properties of other modifications of convex method are considered, especially those based on the definition of imperfection zone marked as a centric hyper-ellipsoid or as an eccentric hyper-ellipsoid. The analytical background was brought up to the level when only a few configurations of imperfections are sufficient to be evaluated numerically. These configurations are obtained by means of the convex analysis as points of extreme critical loading using the Lagrange method of constrained extremes.
Klíčová slova:
convex domain method; system stability; hyper-prism and hyper-ellipsoid domains
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Stability of a bar influenced by small and large imperfections
The geometrical and physical imperfections of systems can drastically reduce their critical loading. These imperfections are usually of stochastic character and, therefore, they act as random ...
Random response of a dynamic system under polynomial of a white noise
Náprstek, Jiří; Fischer, Cyril
2020 - anglický
Many types of external additive random excitation of dynamic systems admit to be modelled as a combination of powers of a Gaussian noise. Such a type of excitation produces a non-Gaussian response even if the dynamic system is linear and the excitation is additive only. Although the excitation as a whole is non-Gaussian, the problem can be transformed into the form of a linear system with an additive and multiplicative white noise excitation which _nally produces a non-Gaussian response. The general method of transformation, the respective FPK equation, basic stochastic moments of the response, and a demonstrative example are discussed.
Klíčová slova:
non-Gaussian excitation; nonlinear filtering; Kronecker algebra
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Random response of a dynamic system under polynomial of a white noise
Many types of external additive random excitation of dynamic systems admit to be modelled as a combination of powers of a Gaussian noise. Such a type of excitation produces a non-Gaussian response ...
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